Chronic hypofusion in the central nervous system, is hypothesized to predispose or lead to Alzheimer's Disease (AD). Increased expression and aggregation of an insoluble peptide, derived through the cleavage of the amyloid precursor protein (APP) by beta and gamma secretases, is thought to initiate plaque formation leading to cell death and the disease state. Hypoxia decreases protein synthesis by inhibiting the cap-binding/scanning mechanism for translation initiation, the major form of translation initiation. However, some mRNAs can also initiate translation in a cap-independent manner from internal ribosomal entry sites (IRESes) in the 5' leader. IRES dependent translation is unaffected or promoted by hypoxia. The hypothesis is that the 5' leaders of mRNAs encoding for proteins that contribute to the processing of APP, as well as APP, contain IRESes. In response to hypoxia, an increase in IRES dependent translation is predicted. Consequently, chronic hypoxia is hypothesized to lead to AD through a constant enhancement of IRESdependent translation with the concomitant increase of amyloid peptides. Accordingly, the proposed study will utilize neural cell lines and primary neurons grown in vitro as an assay system to answer the following questions: 1. Does the 5' leader of the APP mRNA and of the mRNAs encoding for proteins involved in the processing of APP including beta-secretases 1 and 2, and presenilins 1 and 2, contain IRESes? 2. Does hypoxia lead to an increase in IRES-dependent translation mediated by the AD-related 5' leaders? 3. What are the cis-elements in the 5' leaders of AD-related mRNAs that internally initiate translation in response to hypoxia? The proposed experiments will determine the mechanism of translation initiation of AD related mRNAs in response to hypoxia. The results will provide novel insights into the etiology of AD and present new avenues to explore for therapeutic intervention of individuals with AD or other vascular dementias.